초록 ▼

A video detector circuit is disclosed which develops a threshold level from a white or background peak signal in regions of low contrast, and from a combination of both white and black peak levels in regions of high contrast. The circuit is adjustable to compensate for variable affection performance

A video detector circuit is disclosed which develops a threshold level from a white or background peak signal in regions of low contrast, and from a combination of both white and black peak levels in regions of high contrast. The circuit is adjustable to compensate for variable affection performance of the detector.

대표청구항 ▼

A video signal detector for converting analog video signals representing optical reflectance from successive small regions on a document into a digital output signal comprising means for producing an analog video signal that varies in magnitude as a function of optical reflection, means responsive t

A video signal detector for converting analog video signals representing optical reflectance from successive small regions on a document into a digital output signal comprising means for producing an analog video signal that varies in magnitude as a function of optical reflection, means responsive to said video signal for developing a white level peak representative voltage signal, means responsive to said video signal for developing a black level peak representative voltage signal, means responsive to said white level peak representative signal and said black level peak representative signal for developing a threshold level voltage signal, comparing means responsive to said video signal and to said threshold level signal for producing a digital output signal, a diode connected between said black level peak signal developing means and said threshold level signal developing means, said diode being oriented to permit conduction in the presence of black level voltage signals, and means supplying back bias to said diode for preventing conduction therethrough in the presence of relatively small black level voltage signals but permitting conduction therethrough in the presence of relatively large black level voltage signals.